In recent years, as a method and a device for decomposition of a hazardous gas, methods and devices using non-thermal plasma have been proposed. Since the device using non-thermal plasma is simple and the non-thermal plasma is a chemical reaction in which an active species having a high reactivity can be used, the reaction instantaneously proceeds. For this reason, the non-thermal plasma is expected to effectively decompose a hazardous gas in a gas. Further, the non-thermal plasma is easily combined with other techniques. The non-thermal plasma is known to be applicable to various types of combined processes. However, when effective decomposition is not sufficient, a by-product is generated by the decomposition of a hazardous gas. For sufficiently effective decomposition, the input of a large amount of energy is required. In this case, there are problems of generation of nitrogen oxides and a large amount of ozone from air. In order to make a practical application of a technique for removing a hazardous gas in air by the non-thermal plasma, it is an important object to suppress the generation of nitrogen oxides and ozone and to improve the decomposition efficiency of the hazardous gas.
As achievement of such an object, a method for decomposing an ethylene gas using plasma (Patent Literatures 1 and 2), a method for providing a honeycomb-shaped catalyst between a discharge electrode and an earth electrode (ground electrode) (Patent Literature 3), and a method for providing a manganese-based catalyst (Patent Literature 4) have been proposed. Further, a method of further remedying the generation of ozone and the generation of by-products by decomposition of a hazardous gas in the conventional method of using non-thermal plasma in combination with a known catalyst and a device for purifying the hazardous gas (Patent Literature 5) have been proposed.